1. Field of Invention
This invention relates to a process and apparatus for treating vitreous surfaces such as glass. More specifically, it preferably relates to a process for treating the surface of newly formed glass bottles still retaining their heat of formation.
2. Description of the Prior Art
In the prior art, coatings have been applied to vitreous surfaces for various purposes. Such purposes include promoting adhesion between a vitreous surface and another substance, coloring the vitreous surface, controlling reflectance thereof, increasing electrical conductivity over the vitreous surface, increasing strength and durability of articles having such surfaces and increasing abrasion and scratch resistance of the surface.
It is well known in the art that glass derives its strength and durability in part from an unblemished surface. Scratches or flaws in the surface of a glass article substantially reduce its strength and decrease the contact force needed to break the article.
It is also well known that impact resistance of glass is greatest for newly formed articles because their surfaces have not been abraded by handling equipment or contact with other objects.
It is, therefore, an object of the present invention to provide an apparatus and process for coating newly formed glass bottles which will increase resistance to surface scratches and abrasion and thus increase the durability and strength of the bottle.
It is known in the art that bottles may be coated at various points in the processing line. They may be coated immediately after formation, at the hot end of the processing line, and/or at the cold end of the line prior to packaging. Coating at the cold end alone has proved unsatisfactory in that no protection is afforded during the earlier steps of processing where articles may contact machinery or each other and thereby become scratched or checked prior to application of a coating. The earlier in the processing line that a coating is applied, the greater will be the scratch resistance of the surface as it proceeds through that processing line. By coating the article after formation and while it still retains its heat of formation there is less likelihood that the article will be abraded during processing. Greater processing line efficiencies can thus be obtained by placing articles closer together during processing and increasing the speed of conveyors. It is, therefore, a further object of the present invention to carry out coating immediately after formation of the article and while the formed article still retains its heat of formation. It should, however, be understood that the substance of the invention is not limited to this particular mode of operation.
In the prior art, attempts have been made to coat a formed glass article by immersion in a liquid containing a metallic coating material. This method, however, subjects the article to unnecessary stresses and tends to deposit very uneven coatings.
There is also known in the prior art the method of applying the coating in a vapor stream by aiming the vapor stream at the article to be coated. This method has the disadvantages that the vapor is lost to the surrounding environment, polluting same, and that directional control over the vapor and control over vapor concentration is difficult to properly maintain.
Many of the complications of the vapor system were solved by carrying out vapor coating in a vented hood. In general, devices to practice this method relied on sources of vapor emanating from the sidewalls of the hood or from guns placed under the hood. Such methods, however, tend to produce satisfactory coating of sidewalls, but rather unpredictable results on the bottom of the articles being coated.
There is also disclosed in the prior art flame coating methods for applying coatings wherein the coating material is incorporated into a combustible vapor which is thereafter directed toward and burned about the article to be coated. The resulting product is generally unsatisfactory due to a residue which frequently appears on the surface of the coated article.
All of the above mentioned prior art methods have one common and serious disadvantage. Although they provide a satisfactory coating on the surface at which they are directed, the results on other surfaces is unpredictable. The present invention produces predictable and satisfactory results as to bottom and side surfaces.
The prior art has recognized the need for a method which will simultaneously coat both sides and the bottom of a glass container. Since no such method was available, alternate methods were employed to protect the bottom portion of glass articles whose sides were being coated. One such alternate method is shown in U.S. Pat. No. 3,561,940 wherein the conveyor belt is coated by a flame treatment process to prevent the metal of the conveyor from contacting the knurled portion of the bottom of the container.
The principal object and advantage of the present invention, therefore, is to provide a method and apparatus whereby the sides and the lower end of a glass bottle can be simultaneously coated in one operation.